Many large mobile machines such as mining trucks, locomotives, marine applications and the like have recently begun using alternative fuels, alone or in conjunction with traditional fuels, to power their engines. For example, large displacement engines may use a gaseous fuel, alone or in combination with a traditional fuel such as diesel, to operate. Because of their relatively low densities, gaseous fuels, for example, natural gas or petroleum gas, are carried onboard vehicles in liquid form. These liquids, the most common including liquefied natural gas (LNG) or liquefied petroleum gas (LPG), are cryogenically stored in insulated tanks on the vehicles, from where a desired quantity of fuel is pumped, evaporated, and provided to fuel the engine.
The pumps that are typically used to deliver the LNG to the engine of the machine include pistons, which deliver the LNG to the engine. Such piston pumps, which are sometimes also referred to as cryogenic pumps, will often include a single piston that is reciprocally mounted in a cylinder bore. The piston is moved back and forth in the cylinder to draw in and then compress the LNG. Power to move the piston may be provided by different means, the most common being electrical, mechanical or hydraulic power.
One example of a cryogenic pump can be found in U.S. Pat. No. 7,293,418 (the '418 patent), which describes a cryogenic, single-element pump for use in a vehicle. The pump discharges into an accumulator that is located within the tank, and uses a single piston pump that is connected to a drive section via a piston rod. The drive section is disposed outside of the tank.
Pumps such as the pump described in the '418 patent are generally large, heavy and complex, which are due, in part, to the large operating pressures and high volumes of fluid that must be delivered to operate a large displacement engine. Because of the nature of their operation, in that a quantity of fluid is delivered by each stroke, typical systems also require various pressure accumulators and regulators to smooth the supply of gaseous fuel to the engine, which further burdens the vehicles with additional components, cost and complexity.